Constant current system



Nov. 23, 1937. E YOUNG 2,099,716

' CONSTANT CURRENT SYSTEM Original Filed May 12, 1936 20d Q/v I 205 2/97 204' 2/ Patented Nov. 23, 1937 UNITED STATES PATENT OFFICE ONSTANTSYSTEM 0riginal application May 12, 1936, Serial No. 79,329. Divided andthis application April 5,

1937, Serial No. 134,970

1 Claim.

My invention relates generally to electrical control systems, and it hasparticular relation to systems of the constant current type.

In the operation of electric lamps, such as incandescent lamps forstreet lighting and the like, it is desirable that the current be heldconstant, or substantially so, in order to provide the desiredillumination and to prolong the life of the lamps as much as possible.The lamp life is materially decreased by eyen slight increase in currentabove the rated value and it is, therefore, desirable to operate thelamps under such conditions that the rated current value will not beexceeded, even tothe slightest degree. i

For street lighting applications where a large number of lamps isoperated at the same time, it is customary, in many cases, to connectthe lamps in series circuit relation for-'the purpose of reducinginstallation and operating costs to a minimum. Some regulating device isprovided for maintaining the current in the series circuit constantregardless of the number of lamps connected or the voltage of the supplycircuit. Various types of regulating devices may be used. In mycopending application, Serial No. 33,706, flied July 29, 1935, I havedisclosed a monocyclic type of regulator in combination with gridcontrolled arc rectifying tubes which are arranged to control thevoltage applied to the regulator or the current flowing in the loadcircuit as a function of the supply voltage or of the load current.While the various systems there disclosed are satisfactory for certainoperating conditions, I have discovered that they require dependence toa considerable degree on the reliability of the grid controlled arcrectifying tubes for their continued operation and that, if the tubesfail, the entire system may be put out of service until they arereplaced.

It is therefore an object of my invention to provide a constant currentsystem which shall be simple, efficient, and reliable in operation, andwhich may be readily and economically manufactured and installed. v

The principal object of my invention is to provide for preventing thecurrent flow in a circuit requiring constant current from exceeding theconstant value of the current at which the circuit is designed tooperate most efllciently.

, An important object of my invention is to provide for variablyshunting a load circuit connected to a constant current device tomaintain the current in ttlhe load circuit constant regardless ofvariations 1 line voltage applied to the device. A further object of myinvention is to provide for shunting the excess current from a circuitrequiring constant current in such manner that the system can stillfunction even though the ap paratus used should be disabled.

A still further object of my invention is to 5 provide regulating meansfor shunting the excess current from a circuit requiring constantcurrent which will be operative only when the load current tends toexceed the constant value of the current and which will permitfunctioning of the 10 system even thoughv the regulating means may bedisabled.

Still another object of my invention is to pro vide for controlling theconductivity of an electric valve connected across the load terminals of15 a constant current device in accordance with the load current toprevent the load current from exceeding its constant value.

A more specific object of my invention is to provide for controlling theconductivity of a pair of inversely connected electric valves connectedacross the load circuit of a monocyclic square to shunt therethrough allcurrent from the load circuit in excess of the normal constant currentthat would otherwise flow through the load circult.

Other objects of my invention will, in part, be obvious and, in part,appear hereinafter.

My invention, accordingly, is disclosed in the embodiment hereof shownin the accompanying drawing, and it comprises the features ofconstruction, combination of elements, and arrangement of parts whichwill be exemplified in the constructions hereinafter set forth and thescope of the application of which will be indicated in the appendedclaim.

For a more complete understanding of the nature and scope of myinvention, reference may be had to the following detailed descriptiontaken in connection with the accompanying drawing.

The single figure of the drawing is a diagram- Mi; matic view of asystem embodying my invention.

This application is a division of my copending application for Constantcurrent system, Serial No. 79,329, filed May 12, 1936. 5

The commercial power systems of the present day are so arranged andconstructed that the line voltage and frequency are maintained at fairlyconstant values. In order to provide constant current for operating agroup of series con- 50 nected incandescent street lamps, a staticregulator of the monocyclic-type may be provided. As long as the supplyvoltage and frequency remain constant, the current which is supplied bythe monocyclic square will remain constant re- 1 quency, however slight,will cause corresponding changes in the current flowing in they loadcircuit. If the supply voltage is increased over its normal rated value,there will be a corresponding increase in the current flowing in theload circuit, and, as a result, the life of the lamps connected thereinwill be materially shortened. These slight changes in the supply voltagemay be caused by faulty operation of regulating devices or by systemdisturbances which are ordinarily encountered in the operation of suchsystems.

In practicing my invention, I take advantage the normally constantvoltage characteristics of a power transmission system of the presentday. and provide a static regulator of the monocyclic type for supplyingthe required constant current for operating a group of series connectedincandescent lamps. In addition to this apparatus, I provide a variableshunt across the load terminals of the monocyclic square which is calledinto operation only when the current in the load circuit tends to exceedthe normal constant value thereof. At all other times the shunt circuitis ineffective and therefore, if for some reason it should fail, suchfailure would not aflect the energization of the lamps, although theywould be subject to the flow of excess current on increase in the supplyvoltage applied to the monocyclic square.

According to the illustrated embodiment of my invention, I have provideda monocyclic square which may be energized from a three phase source ofalternating current. The load terminals are connected to a circuitincluding the series connected incandescent lamps which may be used forstreet lighting purposes. A pair of inversely connected grid controlledarc rectifying devices is connected across the load circuit, and theconductivity thereof is controlled by means of a phase shifting circuit,the operation of whichi in the load circuit tends to exceed apredetermined value, the arc rectifying devices are rendered conductingto shunt therethrough the excess current. By changing the'time in eachhalf cycle at which each of the arc rectifying devices is renderedconducting in accordance with the excess current which tends to flow inthe load circuit, greater or-less amounts of the current may be shuntedwith the result that the excess current is prevented from flowingthrough the lamp .circuit.

In some applications it is desirable to transform from a three-phasealternating current source into a constant current single-phase loadcircuit comprising the series connected incandescent lamps. Thistransformation can be effected and a balanced load applied on each ofthe phases of the three-phase system by use of the connections shown inthe drawing.

As shown in the drawing, transformer means at is provided, comprisingtwo transformers, one having a primary winding 9i and the other aprimary winding 92, for connection to the three phase source 5! ofalternating current. The primary windings 9| and 92 are connected to thesource M by the well known Scott connection. The terminals of theprimary winding 9| are connected to two of the phases of the'source 5|,while one terminal" of the winding '92 is connected to the remainingphase. The other terminal of the primary winding M is connected to amid-tap 93 on the primary winding 9 l The transformer means 90 isprovided with secondary windings 9d and 95, one for each transformer, inwhich voltages in quadrature with each other will be induced. Thesecondary winding 94 is connected directly across the supply terminalsof a regulator or monocyclic square in, while the secondary winding 95is connected in series circuit relation with the load circuit comprisingconductors i2 and i3 and the series connected incandescent lamps i l,and the combined circuit is connected across the load terminals of themonocyclic square lll as illustrated. Since the voltage appearing acrossthe load terminals of the monocyclic square Iii is in quadrature withthe voltage impressed thereon from the secondary winding 94, the voltageinduced in the secondary winding 95 may be readily combined therewith tocause the flow of constant current through the conductors i2 and itwhile maintaining a balanced load on each of the phases of the source Mas is readily understood by those skilled in the 'art.

As long as the voltage applied by the generator 5i to the regulator I9remains constant, the current which flows through the load circuit tothe lamps It will likewise remain constant. However, if the voltage ofthe generator St, for some reason, tends to rise, there will be acorresponding tendency to increase in the current flowing through theload circuit. This excess current is shunted by means of a pair ofinversely connected arc rectifying devices 29 and N which are connected,as illustrated, between the conductors l2 and i3 and across the loadterminals of the regulator iii. The are rectifying devices or valves 20and 2! are provided, respectively, with anodes 20a 9 and 2 I a, withcathodes 20c and 2lc, which may be of the hot type, and controlelectrodes 20g and 2 ,Since the current in the load circuit ismaintained 'at a substantially constant value, a series transformer,shown generally at 96, may be provided having a primary winding 91connected in the load circuit, and a secondary winding 98. A

grid transformer, shown generally at 22, is provided with secondarywindings and 25 connected to the grid or control electrodes 20g andIiig, respectively. Secondary winding 24 is connected to conductor l3and secondary winding 25 is connected to conductor l2. The primarywinding 26 of the grid transformer 22 is connected for energizationbetween a mid-tap 99 on the secondary winding 98 and a common connection29 between a potentiometer 3|, having. a movable connection 32, and avariable inductor 33. A phase shifting circuit 34, comprising thepotentiometer 3| and the inductor 33, is connected to the ends of thesecondary winding 98.

In order to control the inductance of the inductor 33, a regulator 40 isprovided having an armature 4i forming a movable core within the turnsof the inductor 33. The armature 4| is mounted at one end of a lever arm42 which is pivoted at 33 and has provided at its other end an armatureM, the position of which is controlled by means of a winding 45connected in series circult relation with the conductor l3 as shown. Abiasing spring 46 is provided to cooperate with the armature 44 forcontrolling the position of the armature 4|.

In operation, as long as the current flowing through the lamps I4 andthe winding 45 does not exceed a predetermined value which is the valueat which the lamps I4 operate most efiiciently, the valves 20 and 2|remain in the non-conducting state. This is accomplished by adjustingthe phase shifting circuit 34 so that the control potentials applied tothe control electrodes 20g and 2Ig under these conditions will have suchphase relationship with respect to the corresponding cathodes 20c and 2I that there is no tendency for current to flow therethrough. However,as soon as the current flowing through the lamps I4 and the winding 45tends to exceed a predetermined value, the armature 44 is moved upwardlyagainst the biasing force of the spring 46 to effect a correspondingdownward movement of the armature 4|. The inductance of the inductor 33is then decreased to shift the phase of the voltage which is applied forenergizing the primary winding 26 of the grid transformer 22. This shiftin phase is reflected in the control potential which is applied to thecontrol electrodes 20g and 2|g, so that the valves 20 and 2| arerendered conducting during the half cycles of the alternating currentwhich they are adapted to conduct at times corresponding to the degreeof phase shift. The degree of phase shift will be controlled by theamount of excess current which tends to flow through the lamps |4. Thusmore or less current will be shunted by the valves 20 and 2|, dependingupon the time in each half cycle at which they are rendered conducting.

It will be observed that the valves 20 and 2| are employed only forconducting the excess current which would otherwise flow to the lampsl4. Since this excess current will usually be comparatively slight, thesize or conducting capacity of the valves 20 and 2| need not be verygreat. It is necessary only that they be of such size as to be capableof conducting the excess current which would otherwise flow to the lampsM.

It will also be observed that the lamps. M will function even though oneor both of the valves 20 or 2| should become inoperative. In such case,the excess current, to a greater or lesser extent, would flow throughthe lamps l4, depending upon whether one or both of the valves 20 or 2|became inoperative. Although the life of the lamps I4 would becorrespondingly shortened, they would still be available forillumination purposes, and thus complete reliance for illumination isnot placed on the continuity of functioning of the valves 20 and 2|.

I claim:

A constant current system comprising, in combination, transformer meanshaving primary windings Scott connected to a three phase source ofalternating current and two secondary windings, a monocyclic squareconnected for energization across one of said secondary windings,circuit means for connecting a load circuit requiring substantiallyconstant current across said monocyclic square through the othersecondary wind- 1 ing, variable conducting means directly connectedacross said load circuit, and regulating means disposed to be responsiveto the current flow in said load circuit for controlling theconductivity of said variable conducting means to maintain the loadcurrent substantially constant on variation of the voltage or frequencyof said alternating current source.

HUGH E. YOUNG.

